The valve device includes a valve, for example, having a butterfly shape, and a passage is fully closed by the valve when the valve is located to be perpendicular to the passage at a full-close position. When the valve is rotated in a valve-opening direction from the full-close position, the valve is defined to be located on a plus side from the full-close position. When the valve is rotated in a direction opposite from the valve-opening direction from the full-close position, the valve is defined to be located on a minus side from the full-close position.
Conventionally, an exhaust gas recirculation (EGR) unit is known as a valve device. JP-A-2005-233063 (US 2005/0183705) describes such an EGR unit in which deposit is removed by controlling an actuator of an EGR valve.
When a predetermined condition is met, for example, when an engine is stopped, the actuator actuates the valve to rotate alternately from the plus side to the minus side with respect to the full-close position.
If deposit gets cold while the engine is stopped, the valve may get stuck by cold deposit, and torque generated when the valve is opened may get increased. However, an area around the valve is cleaned by an alternate rotating movement of the valve, because the deposit can be removed.
To practice the deposit removing control, the valve needs to rotate toward the minus side, so a range of rotating of the valve needs to be extended to the minus side, minus ten degree (−10°), for example.
In a conventional technique, a double-spring is applied as a return spring, and the valve is controlled to rotate back to the full-close position. The double-spring includes a first spring and a second spring. The first spring controls the valve to rotate back to the full-close position from the plus side, and the second spring controls the valve to rotate back to the full-close position from the minus side.
The double-spring has a complicated structure in which the first and second springs have opposite winding directions, so producing cost is increased.
Furthermore, the double-spring has three positions to be fixed, so the number of assembly process is increased. The three positions are a free end of the first spring, a free end of the second spring, and a middle hook placed at a connection section of the first spring and the second spring.
On the other hand, when the amount of the deposit is smaller, the deposit removing control is unnecessary. In this case, the valve does not need to rotate toward the minus side.
When the valve rotates from the plus side to the full-close position, it is necessary to reduce rotating speed of the valve to prevent the valve from colliding with a stopper. In other words, speed reducing control of the valve is necessary. In this case, a response to revolve the valve to the full-close position is required to be raised.